Alki Bike and Board has various types of bikes for rent. (I’m checking with them and will update this post once I find out if they rent on somewhere on Alki or if you have to go to their North Admiral location on California).

PS: Although Beach Drive Bungalow is waterfront and located on Puget Sound, it does not have beach access due to the seawall/bulkhead. The Bungalow is located a couple blocks away from public parks with access to the sound.